32 GB, but don't buy one. It comes with a 4 GB card, and the only thing that can go on it is pictures you take with the built in camera. Absolutely ANYTHING you download whether its apps, music, pics, whatever, goes on the internal memory. And there is NO way to transfer data from internal memory to the SD card. It's a pretty bad flaw in the phone, but it is what it is.
I have a 32GB in mine, not sure if it can handle any more than that.